Learner Resource 2
This activity can be used to reinforce learning of gametogenesis and the function of hormones in
both males and females. The boxes can be cut and learners then asked to put them in the correct
sequences – a column for males, a column for females which join at fertilisation to show the events
leading to implantation.
Females
Oogonia (diploid) are present in the ovaries of a fetus before birth, held at
prophase I of meiosis.
At puberty, Gonadotrophin releasing hormone (GnRH) is released into the
blood. It stimulates the release of LH and FSH from the anterior pituitary
gland.
FSH and LH levels rise in the bloodstream binding to follicle cells in the
ovary which are stimulated to produce oestrogen.
One follicle becomes dominant and the primary oocyte (diploid) it completes
meiosis I to produce a secondary oocyte (haploid).
The dominant follicle, known as the Graffian follicle secretes increasing
amounts of oestrogen, which initially inhibits FSH and LH but then
stimulates a surge of LH causing ovulation – the dominant follicle releases
the secondary oocyte.
After ovulation, the secondary oocyte proceeds to the end of meiosis II to
produce a mature ovum which passes into the oviduct. The follicle remains
in the ovary as the Graffian follicle and secretes progesterone.
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Males
At puberty, Gonadotrophin releasing hormone (GnRH) is released into the
blood. It stimulates the release of LH and FSH from the anterior pituitary
gland.
LH binds to receptors on the Leidig cells which then secrete testosterone.
Testosterone affects sertoli cells in the testes, which stimulates
spermatogenesis. Excessive production of sperm is prevented by negative
feedback – high levels of testeoterone cause the production of inhibin.
During spermatogenesis, spermatogonia (diploid) in the seminiferous
tubules divide by mitosis to produce primary spermatocytes (diploid) and
then by meiosis I to produce secondary spermatocytes (haploid).
Secondary spermatocytes undergo meiosis II producing spermatids which
mature into spermatozoa and are stored as haploid sperm in the epididymis.
At ejaculation, sperm are released into the vas deferens, fluids are added
from the seminal vesical and prostate gland. The resulting semen is
released through the urethra.
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Fertilisation
Semen enters the vagina, passing through the cervix, uterus and into the
fallopian tube
Fertilisation occurs when the sperm nucleus enters the ovum, meiosis II is
completed in the ovum and the nuclei form the sperm and ovum fuse to
produce a zygote (diploid).
The zygote undergoes rapid mitosis forming a blastocyst which implants in
the endometrium of the uterus and secretes HCG which can be detected in
a pregnancy test.
OCR Resources: the small print
OCR’s resources are provided to support the teaching of OCR specifications, but in no way constitute an endorsed teaching method that is required by the Board, and the decision to
use them lies with the individual teacher. Whilst every effort is made to ensure the accuracy of the content, OCR cannot be held responsible for any errors or omissions within these
resources.
© OCR 2016 - This resource may be freely copied and distributed, as long as the OCR logo and this message remain intact and OCR is acknowledged as the originator of this work.
OCR acknowledges the use of the following content:
Please get in touch if you want to discuss the accessibility of resources we offer to support delivery of our qualifications: resources.feedback@ocr.org.uk
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